Investments and Derivative Instruments (Details 19) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional Amount	$ 151,155	$ 141,436
Fair Value	(1,045)	(458)
Credit [Member]
Derivative [Line Items]
Notional Amount	7,324	7,046
Fair Value	(100)	(305)
Offsetting Notional Amount	4,322	4,094
Offsetting Fair Value	46	107
Corporate Credit/Foreign Gov. [Member] | Single Name Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	1,693	1,628
Fair Value	(12)	(34)
Weighted Average Years to Maturity	3 years	3 years
Underlying Referenced Credit Obligation Type	Corporate Credit/ Foreign Gov.	Corporate Credit/ Foreign Gov.
Average Credit Rating	A	A+
Offsetting Notional Amount	1,424	1,424
Offsetting Fair Value	(29)	(15)
Corporate Credit [Member] | Single Name Credit Default Swaps [Member] | Below Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	160	170
Fair Value	(2)	(7)
Weighted Average Years to Maturity	2 years	2 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BB-	BB-
Offsetting Notional Amount	144	144
Offsetting Fair Value	(5)	(5)
Corporate Credit [Member] | Basket Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	3,866	3,645
Fair Value	(6)	(92)
Weighted Average Years to Maturity	3 years	3 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BBB+	BBB+
Offsetting Notional Amount	2,229	2,001
Offsetting Fair Value	0	29
Corporate Credit [Member] | Basket Credit Default Swaps [Member] | Below Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	555	553
Fair Value	(465)	(509)
Weighted Average Years to Maturity	3 years	3 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BBB	BBB+
Offsetting Notional Amount	0	0
Offsetting Fair Value	0	0
Corporate Credit [Member] | Embedded Credit Derivatives [Member] | Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	25	25
Fair Value	24	24
Weighted Average Years to Maturity	3 years	3 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BBB-	BBB-
Offsetting Notional Amount	0	0
Offsetting Fair Value	0	0
Corporate Credit [Member] | Embedded Credit Derivatives [Member] | Below Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	500	500
Fair Value	441	411
Weighted Average Years to Maturity	5 years	5 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BB+	BB+
Offsetting Notional Amount	0	0
Offsetting Fair Value	0	0
CMBS Credit [Member] | Basket Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member] | Credit [Member]
Derivative [Line Items]
Notional Amount	525	525
Fair Value	(80)	(98)
Weighted Average Years to Maturity	5 years	5 years
Underlying Referenced Credit Obligation Type	CMBS Credit	CMBS Credit
Average Credit Rating	A	BBB+
Offsetting Notional Amount	525	525
Offsetting Fair Value	$ 80	$ 98